Sera Monastery was founded in 1419 by a disciple of Tsongkhapa, who was the creator of the Yellow Hat Sect. The dwelling sits on the northern outskirts of Lhasa and contains three colleges dedicated to esoteric Tantric study. Originally housing around 5,000 monks, the population is now down to 600. The largest building, the Great Assembly Hall houses huge tangkas, Buddhist banners. Sera, along with Drepung and Ganden Monasteries served as the three "pillars of the Tibetan state."